To the Editor.—The review of R. Joe Noble, MD, "The Patient With Syncope" (237:1372, 1977), is timely and quite helpful. However, two points require comment for different reasons.

The first has its obvious bedside diagnostic implications; while lack of increase of heart rate with drop of blood pressure points to autonomic dysfunction, tachycardia on standing does not exclude a diagnosis of idiopathic orthostatic hypotension.1 In contrast to usual teaching, heart rate in this disorder does vary in many patients with head-up tilt.2 Cardiac nerves may not be involved until later in the evolution of the disease.

The second concerns the value of plasma renin activity (PRA) in the localization of the neurologic defect. The distinction made in the diagram is based on one report3 that has not been confirmed; in fact, our experience4 and that of others is that PRA can increase with